Instances can go down, disappear or be unresponsive due to many reasons.
Go to your account settings now and export your account settings!
This file contains your subscriptions, follows, profile settings etc. It’s very easy to start over on a new instance when you have your export file.
Back it up, export it, save it, repeat occasionally.
@general@lemmy.world
Just an addendum so Fediverse newcomers don’t assume things from your “etc.”: one’s own old posts/replies can’t be transferred across accounts, at least not without republishing, IIRC. There are Fediverse platforms that allows for “importing” these from an old account (the platform I use, a Misskey fork, has this feature), but all it does is republishing anew, as neither authorship nor timestamp from old activities are reassignable, as per ActivityPub standards. To complicate things, republishing isn’t something nice to do when the person has a history comprised of thousands of activities, including replies/threads where handles for Lemmy communities are mentioned (so I guess each post would end up as new, repeated threads/replies across the threadiverse).
I say this because I’m currently facing this exact conundrum myself: for almost a year, I’ve had a Calckey account (@dsilverz@calckey.world) from which I’ve posted a thousand notes, (mostly) including interactions with Lemmy and hundreds of microblogging, but then the instance I was housed in started getting some issues beyond the scope of this reply (rule 5). I saw myself in need of seeking another instance, one that uses the same platform (because I liked Misskey, its features and how it allows for having both threadiverse communities alongside a personal feed), and I found the nice Catodon instance I’m currently housed in.
I was able to easily customize my new account’s settings with the same settings that of my earlier account (because both platforms share the same Misskey origins), including the vampe UI theme I use, but the only thing I can practically do regarding my thousand posts is exporting these as a JSON and redownloading their media in some kind of post-mortem archive, because even republishing my microblogging posts would be unfeasible (I mean, technically speaking I could, it doesn’t mean I should, because it’d end up as a flood of posts, so I’m not doing it).